The use of bone pins and plates for reducing fractures is well known in orthopedic medicine. The pins and plates extend across discontinuities in a bone to fix the broken ends in relation to each other to reduce pain and promote rapid healing without deformity. These devices are secured to the bone by bone screws or nails driven into the bone. More recently, pins, rods, plates and cages have been used to stabilize bone and joints that have deteriorated naturally or as a result of prior trauma.
The interface between the bone screws and the bone presents problems of stability and long term usage that have been addressed in different ways. One of the major problems is usually termed as back-out. This defines the condition in which the fastening devices attaching the plate to the bone loosen over time, either relative to the bone or the plate or both. Severe back-out results in the bone screw working itself out of the bone and/or plate resulting in instability of the bone or joint. This situation results in increasing pain and danger from the instability, as well as, the movement of the screw. There may be several reasons for the back-out but anatomical stresses from body movements contributes greatly to the problem.
Spinal bone plates are usually attached to adjacent vertebrae to reduce pain due to injury or deterioration of the intermediate disk. The plate spans the intervertebral space to stabilize the vertebrae. Pedicle screws or bone screws are inserted through apertures in the opposite ends of the plate into the respective vertebrae or on opposite sides of a break. Due to anatomical forces on the skeleton, the screws sometimes back out of the bones and plates.
What is needed in the art is a bone plate with an internal screw lock that rotates to wedge the bone screws to the plate. Also, an arrangement of the bone screws to permit the use of a narrow bone plate.